[libcxx] Fix build bustage with threads disabled

[glandium]

Summary

Building with -DLIBCXX_ENABLE_THREADS=OFF -DLIBCXXABI_ENABLE_THREADS=OFF
(like e.g. for wasm) fails after D146228 because of a misplaced std
namespace begin/end.

[philnik]

Could you maybe give a few more specifics about what the problem is? Not opening the namespace shouldn't result in an error, and we do it this way in lots of places.

[philnik]

I see the problem now. The #ifdef _LIBCPP_HAS_NO_THREADS is split in the middle of the file, which results in a function being defined in the global namespace instead of the standard one. LGTM.

libcxx/include/__condition_variable/condition_variable.h

 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #  pragma GCC system_header
 #endif
 
 _LIBCPP_PUSH_MACROS
 #include <__undef_macros>
 
-#ifndef _LIBCPP_HAS_NO_THREADS
-
 _LIBCPP_BEGIN_NAMESPACE_STD
 
+#ifndef _LIBCPP_HAS_NO_THREADS
+
 // enum class cv_status
 _LIBCPP_DECLARE_STRONG_ENUM(cv_status){no_timeout, timeout};
 _LIBCPP_DECLARE_STRONG_ENUM_EPILOG(cv_status)
 
 class _LIBCPP_TYPE_VIS condition_variable {
   __libcpp_condvar_t __cv_ = _LIBCPP_CONDVAR_INITIALIZER;
 
 public:

 #  endif // _LIBCPP_HAS_COND_CLOCKWAIT
 
 template <class _Clock>
 inline void condition_variable::__do_timed_wait(unique_lock<mutex>& __lk,
                                                 chrono::time_point<_Clock, chrono::nanoseconds> __tp) _NOEXCEPT {
   wait_for(__lk, __tp - _Clock::now());
 }
 
-_LIBCPP_END_NAMESPACE_STD
-
 #endif // _LIBCPP_HAS_NO_THREADS
 
+_LIBCPP_END_NAMESPACE_STD
+
 _LIBCPP_POP_MACROS
 
 #endif // _LIBCPP___CONDITION_VARIABLE_CONDITION_VARIABLE_H